Read window budget based dynamic program step characteristic adjustment

ABSTRACT

A read window budget (RWB) corresponding a group of memory cells is determined. The determined RWB and a target RWB is compared. In response to the determined RWB being different than the target RWB, one or more program step characteristics are adjusted to adjust the determined RWB toward the target RWB.

TECHNICAL FIELD

Embodiments of the disclosure relate generally to memory sub-systems,and more specifically, relate to read window budget based dynamicprogram step characteristic adjustment.

BACKGROUND

A memory sub-system can be a storage system, such as a solid-state drive(SSD), and can include one or more memory components that store data.The memory components can be, for example, non-volatile memorycomponents and volatile memory components. In general, a host system canutilize a memory sub-system to store data at the memory components andto retrieve data from the memory components.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure will be understood more fully from the detaileddescription given below and from the accompanying drawings of variousembodiments of the disclosure.

FIG. 1 illustrates an example computing environment that includes amemory sub-system in accordance with some embodiments of the presentdisclosure.

FIG. 2 illustrates an example of programming memory cells in accordancewith some embodiments of the present disclosure.

FIG. 3 illustrates threshold voltage distributions associated with aprogramming process in accordance with some embodiments of the presentdisclosure.

FIG. 4 illustrates a read window between threshold voltage distributionscorresponding to memory cells programmed in accordance with someembodiments of the present disclosure.

FIG. 5A-5B illustrate example programming steps whose characteristicscan be adjusted in association with adjusting a read window budget inaccordance with some embodiments of the present disclosure.

FIG. 6 is a graph illustrating how adjusting one or more program stepcharacteristics affects the read window budget in accordance with someembodiments of the present disclosure.

FIG. 7 is a diagram illustrating how adjusting one or more program stepcharacteristics affects the read window budget in accordance with someembodiments of the present disclosure.

FIG. 8 is a diagram illustrating how adjusting one or more program stepcharacteristics affects the read window budget in accordance with someembodiments of the present disclosure.

FIG. 9 is a flow diagram of an example method corresponding to adjustinga read window budget in accordance with some embodiments of the presentdisclosure.

FIG. 10 is a flow diagram of an example method corresponding toadjusting a read window budget in accordance with some embodiments ofthe present disclosure.

FIG. 11 is a block diagram of an example computer system in whichembodiments of the present disclosure can operate.

DETAILED DESCRIPTION

Aspects of the present disclosure are directed to managing read windowbudget within a memory sub-system. A memory sub-system is alsohereinafter referred to as a “memory device.” An example of a memorysub-system is a storage system, such as a solid-state drive (SSD). Insome embodiments, the memory sub-system is a hybrid memory/storagesub-system. In general, a host system can utilize a memory sub-systemthat includes one or more memory components. The host system can providedata to be stored at the memory sub-system and can request data to beretrieved from the memory sub-system.

In various memory sub-systems, programming cells can involve providing aprogramming signal to a group of cells (e.g., a page) to place them intarget states, which correspond to respective stored data patterns. Forexample, the cells can be non-volatile flash memory cells configured tostore one or more bits of data per cell. As an example, a programmingsignal used to program the cells can comprise a stepped voltage signal(e.g., voltage ramp) with each step having an associated step size andduration. The programming signal can be applied (e.g., to a word line)as a series of voltage pulses, for instance. The voltage pulses havevarious characteristics which can affect a read window budget (RWB)associated with the programmed cells. An RWB can refer to the cumulativevalue (e.g., in voltage) of a number (e.g., seven) of distances (e.g.,in voltage) between adjacent threshold voltage distributions at aparticular BER. Such characteristics include pulse magnitude, step sizebetween pulses (e.g., program step size), and pulse duration (e.g.,program step duration), among various other characteristics. As usedherein, a program step size can be referred to as a voltage differencebetween successive voltage pulses, and a program step duration can bereferred to as a duration for which a voltage pulse is applied. Inrelation to program step duration, in at least one example, program stepduration can be measured by counting clock cycles of a known frequencybetween a time a program command was issued to a memory (e.g., NAND) andwhen the memory programming operation is complete. In another example,the program step duration can be measured by using a number of programpulses used to complete the memory program operation and apply a knownamount of time for each pulse.

As described further herein, a read window, which may be referred to asa read window width, refers to a distance (e.g., in voltage) betweenadjacent threshold voltage (Vt) distributions at a particular bit errorrate (BER). A read window may also be referred to as a “valley margin”since the Vt distributions include respective peaks with the regionstherebetween being referred to as valleys. The RWB can refer to acumulative value of read windows for a group of programmed cells (e.g.,one or more pages of cells). For example, cells configured to storethree bits of data per cell may be programmed to one of eight differentVt distributions, each corresponding to a respective data state. In thisexample, the RWB can be the cumulative value (e.g., in voltage) of theseven read windows between the eight Vt distributions. The RWBcorresponding to a group of memory cells is affected by various factorssuch as temperature, wear cycling (e.g., program/erase cycles), etc.Therefore, the RWB(s) of a system can vary over time, which can affectsystem quality of service (QoS), reliability, and/or performance. Invarious instances, it can be beneficial to maintain a specified RWB inorder to maintain a particular system characteristic (e.g., QoS, errorrate, etc.) across various environmental conditions and/or userworkloads. However, it can also be beneficial to provide the ability todynamically adjust a RWB (e.g., to a target value) in order to changeone or more system characteristics. For instance, it may be beneficialto provide one system, or components thereof, with a relatively high RWBassociated with high reliability (e.g., low bit error rate) and anothersystem, or components thereof, with a relatively low RWB associated withhigher speed. It can also be beneficial to adjust the RWB of aparticular system or component thereof such that the system operates atdifferent reliability levels and speed at different times.

Conventional memory sub-systems do not dynamically adjust RWB and/or arenot capable of adjusting the RWB in a predictable and/or controllablemanner. Therefore, various conventional systems are not able to, forexample, maintain a target RWB with changing temperature and/orprogram/erase cycling.

In contrast, embodiments of the present disclosure address the above andother deficiencies by providing a memory sub-system capable of finelycontrolling (e.g., tuning) a RWB in a more efficient manner as comparedto previous approaches. For example, embodiments are capable of toachieving and maintaining a target RWB by modifying one or morecharacteristics of voltage signals (e.g., pulses) used to program memorycells. Such a memory sub-system can provide various benefits such asthose described above. For instance, embodiments can control a RWB tomaintain a particular level of quality, reliability, and/or performanceof the system in various environmental conditions and/or user workloads.

FIG. 1 illustrates an example computing environment 101 that includes amemory sub-system 104 in accordance with some embodiments of the presentdisclosure. The memory sub-system 104 can include media, such as memorycomponents 110. The memory components 110 can be volatile memorycomponents, non-volatile memory components, or a combination of such. Insome embodiments, the memory sub-system is a storage system. An exampleof a storage system is a SSD. In some embodiments, the memory sub-system104 is a hybrid memory/storage sub-system. In general, the computingenvironment 100 can include a host system 102 that uses the memorysub-system 104. For example, the host system 102 can write data to thememory sub-system 104 and read data from the memory sub-system 104.

The host system 102 can be a computing device such as a personal laptopcomputer, a desktop computer, a digital camera, a mobile telephone, or amemory card reader, among various other types of hosts. The host system102 can include or be coupled to the memory sub-system 104 (e.g., via ahost interface 106) so that the host system 120 can read data from orwrite data to the memory subsystem 104. As used herein, “coupled to”generally refers to a connection between components, which can be anindirect communicative connection or direct communicative connection(e.g., without intervening components), whether wired or wireless,including connections such as electrical, optical, magnetic, etc. Thehost interface 106 can be a physical interface, examples of whichinclude, but are not limited to, a serial advanced technology attachment(SATA) interface, a peripheral component interconnect express (PCIe)interface, universal serial bus (USB) interface, Fibre Channel, SerialAttached SCSI (SAS), etc. The host interface 106 can be used to transmitdata between the host system 120 and the memory sub-system 104. The hostsystem 102 can further utilize an NVM Express (NVMe) interface to accessthe memory components 110 when the memory sub-system 104 is coupled withthe host system 102 by a PCIe interface. The physical host interface canprovide an interface for passing control, address, data, and othersignals between the memory sub-system 104 and the host system 102. Thememory components 110 can include a number of arrays of memory cells(e.g., non-volatile memory cells). The arrays can be flash arrays with aNAND architecture, for example. However, embodiments are not limited toa particular type of memory array or array architecture. Althoughfloating-gate type flash memory cells in a NAND architecture aregenerally referred to herein, embodiments are not so limited. The memorycells can be grouped, for instance, into a number of blocks including anumber of physical pages. A number of blocks can be included in a planeof memory cells and an array can include a number of planes. As oneexample, a memory device can be configured to store 8 KB (kilobytes) ofuser data per page, 128 pages of user data per block, 2048 blocks perplane, and 16 planes per device. The memory components 110 can alsoinclude additionally circuitry (not illustrated), such as controlcircuitry, buffers, address circuitry, etc.

In operation, data can be written to and/or read from memory (e.g.,memory components 110 of system 104) as a page of data, for example. Assuch, a page of data can be referred to as a data transfer size of thememory system. Data can be sent to/from a host (e.g., host 102) in datasegments referred to as sectors (e.g., host sectors). As such, a sectorof data can be referred to as a data transfer size of the host.

The memory components 110 can include various combinations of thedifferent types of non-volatile memory components and/or volatile memorycomponents. An example of non-volatile memory components includes anegative-and (NAND) type flash memory. The memory components 110 caninclude one or more arrays of memory cells such as single level cells(SLCs) or multi-level cells (MLCs) (e.g., triple level cells (TLCs) orquad-level cells (QLCs)). In some embodiments, a particular memorycomponent can include both an SLC portion and a MLC portion of memorycells. Each of the memory cells can store one or more bits of data(e.g., data blocks) used by the host system 102. Although non-volatilememory components such as NAND type flash memory are described, thememory components 110 can be based on various other types of memory suchas a volatile memory. In some embodiments, the memory components 110 canbe, but are not limited to, random access memory (RAM), read-only memory(ROM), dynamic random access memory (DRAM), synchronous dynamic randomaccess memory (SDRAM), phase change memory (PCM), magneto random accessmemory (MRAM), negative-or (NOR) flash memory, electrically erasableprogrammable read-only memory (EEPROM), and a cross-point array ofnon-volatile memory cells. A cross-point array of non-volatile memorycan perform bit storage based on a change of bulk resistance, inconjunction with a stackable cross-gridded data access array.Additionally, in contrast to many flash-based memories, cross-pointnon-volatile memory can perform a write in-place operation, where anon-volatile memory cell can be programmed without the non-volatilememory cell being previously erased. Furthermore, the memory cells ofthe memory components 110 can be grouped as memory pages or data blocksthat can refer to a unit of the memory component used to store data.

As illustrated in FIG. 1, the memory sub-system 104 can include acontroller 108 coupled to the host interface 106 and to the memorycomponents 110 via a memory interface 111. The controller 108 can beused to send data between the memory sub-system 104 and the host 102.The memory interface 111 can be one of various interface types compliantwith a particular standard such as Open NAND Flash interface (ONFi).

The controller 108 can communicate with the memory components 110 toperform operations such as reading data, writing data, or erasing dataat the memory components 110 and other such operations. The controller108 can include hardware such as one or more integrated circuits and/ordiscrete components, a buffer memory, or a combination thereof. Thecontroller 108 can be a microcontroller, special purpose logic circuitry(e.g., a field programmable gate array (FPGA), an application specificintegrated circuit (ASIC), etc.), or other suitable processor. Thecontroller 108 can include a processing device 112 (e.g., processor)configured to execute instructions stored in local memory 109. In theillustrated example, the local memory 109 of the controller 108 includesan embedded memory configured to store instructions for performingvarious processes, operations, logic flows, and routines that controloperation of the memory sub-system 104, including handlingcommunications between the memory sub-system 104 and the host system102. In some embodiments, the local memory 109 can include memoryregisters storing memory pointers, fetched data, etc. The local memory109 can also include read-only memory (ROM) for storing micro-code.

While the example memory sub-system 104 in FIG. 1 has been illustratedas including the controller 108, in another embodiment of the presentdisclosure, a memory sub-system 104 may not include a controller 108,and can instead rely upon external control (e.g., provided by anexternal host, such as by a processing device separate from the memorysub-system 104).

The controller 108 can use and/or store various operating parametersassociated with operating (e.g., programming and/or reading) the memorycells. Such operating parameters may be referred to as trim values andcan include programming pulse magnitude, step size, pulse duration,program verify voltages, read voltages, etc. for various differentoperating processes. The different processes can include processes toprogram cells to store different quantities of bits, and differentmultiple pass programming process types (e.g., 2-pass, 3-pass, etc.).The controller 108 can be responsible for other operations such as wearleveling operations, garbage collection operations, error detectionand/or correction (e.g., error-correcting code (ECC)) operations,encryption operations, caching operations, and address translationsbetween a logical block address and a physical block address that areassociated with the memory components 110.

The memory sub-system 104 can also include additional circuitry orcomponents that are not illustrated. For instance, the memory components110 can include control circuitry, address circuitry (e.g., row andcolumn decode circuitry), and/or input/output (I/O) circuitry by whichthey can communicate with controller 108 and/or host 102. As an example,in some embodiments, the address circuitry can receive an address fromthe controller 108 and decode the address to access the memorycomponents 110.

In various embodiments, the controller 108 can include a RWB adjustmentcomponent 113 that controls and/or communicates with a program stepcharacteristic component 115 to determine and/or control one or moreprogram step characteristics used to program cells. The program stepcharacteristics can include, for example, various characteristics ofvoltage pulses used to program memory cells of the memory components110. The characteristic can be, for example, a step size (e.g., voltagedifference) between programming voltage pulses (e.g., betweenconsecutive pulses). In another example, the characteristic can be aduration for which programming voltage pulse(s) are applied to memorycells. The memory cells can be programmed, for example, via anincremental step pulse programming (ISPP) process in which a series ofpulses of increasing magnitude are applied to the cells (to their gates)to increase the stored charge by a particular amount until the targetstored threshold voltage (Vt) is reached. For instance, FIG. 2illustrates threshold voltage (Vt) distributions of cells, whichcorrespond to the charge stored on the charge storage structures of thememory cells, at various stages of one such incremental programmingoperation. Stage 214 can represent a time at which the programmingoperation begins. Accordingly, as shown by Vt distribution 216, the Vtof all the cells is below the target Vt level (Vtarget) 229. To programthe memory cells to the desired target Vtarget 229, a series ofprogramming steps (e.g., voltage pulses) can be used at each of a numberof subsequent stages 218, 222 and 226 to increase the cell Vt levels asshown by distributions 220, 224 and 228, respectively. After eachprogramming step, a program verify operation can be performed to verifywhether the cells being programmed have reached Vtarget 229. As shown inFIG. 2, programming of the cells is completed at stage 226, as the Vtlevels of all the cells have been increased to at or above the desiredtarget Vt level 229.

The amount by which the Vt distributions 216, 220, 224, and 228 increaseresponsive to an applied programming pulse can depend on various factorssuch as the magnitude of the pulse and the duration for which the pulseis applied to the cells. Accordingly, the time to program a group ofcells to desired states can vary depending upon the programming signalcharacteristics as well as the quantity of pulses. Additionally, asdescribed further below, multiple programming passes can be used toprogram multiple logical page data to cells. For example, a first pass,which can be referred to as a lower page programming process, can beused to program one or more lower pages of data to a group of cells, andone or more subsequent programming passes can be used to programadditional pages of data to the group of cells.

The diagram shown in FIG. 3 illustrates threshold voltage (Vt)distributions associated with a programming process in accordance withembodiments of the present disclosure. In this example, the process is atwo-pass programming process in which a lower page (e.g., leasesignificant bit) of a group of memory cells is programmed in a firstprogramming pass and an upper page (e.g., middle bit) and extra page(e.g., most significant bit) of the group are programmed in a secondprogramming pass. The first programming pass can be referred to as alower page programming (LPP) process 325, and the second programmingpass can be referred to as an upper page programming and extra pageprogramming process (UPP/EPP) 329.

As described further below, each of the LPP process 325 and UPP/EPPprocess 329 can involve application of a series of programming pulses toa selected word line corresponding to the group of cells beingprogrammed. As part of the LPP process 325, the Vt of the memory cellsare adjusted (e.g., from an erased Vt level) to one of two levelsrepresented by Vt distributions 330-1 and 330-2. The voltage levels arerepresented by Vt distributions, which can reflect a statistical averageVt level of cells programmed to a particular level. In this example,cells whose lower page is to store a bit value of “1” (e.g., LP=1) areprogrammed to distribution 330-1 during LPP process 325, and cells whoselower page is to store a bit value of “0” (e.g., LP=0) are programmed todistribution 330-2 during LPP process 325. A lower page is a lower orderpage and is programmed in the array of memory cells before higher orderpages are programmed.

As part of the UPP/EPP process 329, the Vt of the memory cells areadjusted to one of eight levels represented by Vt distributions 334-1 to334-8, which correspond to data states E1 to E8, respectively, with eachone of the data states E1 to E8 representing a different 3-bit storeddata pattern. In this example, cells programmed to data state E1 storedata “111,” cells programmed to data state E2 store data “011,” cellsprogrammed to data state E3 store data “001,” cells programmed to datastate E4 store data “101,” cells programmed to data state E5 store data“100,” cells programmed to data state E6 store data “000,” cellsprogrammed to data state E7 store data “010,” and cells programmed todata state E8 store data “110.” While the example illustration includesa 2-pass programming, this is but one example. Additional quantities ofprogram passes can be used.

FIG. 3 also illustrates the read windows (e.g., 336-1, 336-2, 336-3,336-4, 336-5, 336-6, and 336-7) referred to collectively as read windows336, corresponding to the data states E1 through E8 (e.g., respective Vtdistributions 334-1 through 334-8). The read window budget for cellsprogrammed to one of states E1 to E8 can refer to the sum of the readwindows 336. As described below in association with FIG. 4, respectiveread windows can be measured at a particular (e.g., target) BER (e.g.,BER 443 shown in FIG. 4).

Particular read windows 336 and/or a RWB can be determined for a groupof memory cells. The group of cells can be, for example one or morepages of cells of the memory components 110. The group of cells can alsobe one or more blocks of memory cells, such as blocks of cells erasedtogether in a particular erase operation. The one or more pages and/orthe one or more blocks can be from a particular memory component (e.g.,die) or from multiple dies. The group of memory cells for which a RWB isdetermined can be randomly selected or can be all of the pages of amemory component (e.g., 110) or system (e.g., 104), for instance;however, embodiments are not so limited. As described further herein, ina number of embodiments, a determined RWB can be adjusted (e.g.,increased or decreased) by adjusting one or more programming pulsecharacteristics to achieve a target RWB for the group of memory cells.For example, the determined RWB can be compared to the target RWB, andat least one of a program step size and a program step duration can beadjusted in order to move the measured RWB toward the target RWB.Further details of measuring and adjusting the RWB is described below inconnection with FIG. 4-10.

FIG. 4 illustrates a read window 436 between threshold voltage (Vt)distributions 440-1 and 440-2 of memory cells programmed in accordancewith some embodiments of the present disclosure. The example Vtdistributions 440-1 and 440-2 (collectively referred to as Vtdistributions 440) can be analogous to the Vt distributions shown inFIG. 3 (e.g., Vt distributions 334-1 334-8) and can correspond to aparticular page of memory cells.

As illustrated in FIG. 4, the read window 436 can be a distance betweenadjacent edges of the Vt distributions 440-1 440-2. The read windowbetween Vt distributions can be calculated, for example, by determininga location of the Vt distribution edges (e.g., on x-axis) by performingmultiple read operations on a page of programmed cells using differentread voltages and monitoring the bit error rate to determine the readvoltage at which a minimum BER occurs for the page. In a number ofembodiments, and as described in FIG. 4, a read window (e.g., 446)between adjacent Vt distributions (e.g., 440-1 and 440-2) can bedetermined based on a particular (e.g., target) BER for a page of cells.The target BER for purposes of read window determination can be userselected and can be 1E-3 or 1E-4, for instance. As an example,determining the read window 446 can include reading the page of cellsusing a first read voltage 444 (shown as “sample 1”). The first readvoltage 444 can be a trim value used to distinguish between cellsprogrammed to state 440-1 and state 440-2. In this example, the readusing read voltage 444 results in a BER below the target BER. Asubsequent read of the page of cells using a different (e.g., lower)read voltage 442 (shown as “sample 2”) is performed. In this example,the read at 442 results in a BER above the target BER. Since the read atread voltage 442 corresponds to a BER above the target BER and the readat read voltage 444 corresponds to a BER below the target BER, thex-axis location (e.g., voltage) corresponding to the target BER 443 canbe determined by interpolating between sample 1 and sample 2.

For the above example, the interpolation between sample 1 and sample 2to determine the relative x-axis location corresponding to the targetBER (e.g., “TargetBERx”) can be demonstrated by the formula:

TargetBERx=Sample1+[(TargetBER−Sample1BER)/(Sample2BER−TargetBER)]

where “Sample1” is the read voltage 444 used for sample 1, “Sample1BER”is the BER determined for the read using read voltage 444 and“Sample2BER” is the BER determined for the read using read voltage 442.

A similar method can be employed to determine the x-axis locationcorresponding to the target BER for Vt distribution 440-2. Therefore,the read window 436 can be determined based on the difference betweenadjacent edges of Vt distributions 440-1 and 440-2 at the target BER443. As described herein, the read window such as read window 436 can besummed with other read windows corresponding to a group (e.g., page) ofcells to constitute an overall RWB. In various embodiments of thepresent disclosure, a determined (e.g., measured) RWB budget can becompared to a target RWB, and programming signal characteristics such asstep size and/or step duration can be adjusted in order to achieve thetarget RWB. As an example, the step size and/or step duration can beadjusted (e.g., increased or decreased) each by a respective particularamount in response to determining that the determined RWB satisfies athreshold (is above or below the threshold value) associated with thetarget RWB.

FIG. 5A-B each illustrate example programming signals in accordance withembodiments of the present disclosure. The example illustrationsrepresent programming pulses applied to memory cells (e.g., to theirgates) to increase the cell threshold voltages (Vts) to target levels.FIG. 5A illustrates a number of pulses P1, P2, and P3 associated with aprogramming operation having a particular program effective time (PET)550. As shown in FIG. 5A, each pulse has a pulse duration 546, which maybe referred to as a program step duration, and a program step size 548between consecutive pulses.

The PET 550 can be associated with a series of pulses (e.g., P1, P2, P3)applied to a group of cells to place the cells of the group inrespective target states. For example, the PET 550 can correspond forthe amount of time to program each of a group of cells to one of thestates E1 to E8 shown in FIG. 3. Memory systems in accordance withembodiments described herein can dynamically adjust (e.g., increase ordecrease) the programming step size 548 and/or step duration 546 inorder to achieve a desired RWB adjustment (e.g., to maintain a desiredRWB). In at least one example, this dynamic increase or decrease can beperformed by the program step characteristic component 115 todynamically adjust or calibrate the programming step size 548 and/orduration 546.

FIG. 5B illustrates the programming operation shown in FIG. 5A afterimplementing a programming step adjustment. For comparison, the previousprogram step size and program step durations, such as 548 and 546,respectively, in FIG. 5A, are illustrated. The adjusted program stepsize 554 is a calibrated or changed instance of the program step size548 for replacing the program step size 548. The adjusted program stepsize 554 is illustrated as being greater than the program step size 548,however, adjustments can be an increase or a decrease in the programstep size. Likewise, the adjusted program step duration 556 is acalibrated or changed instance of the program step duration 546 forreplacing the program step duration 546. The adjusted program stepduration 556 is illustrated as being greater than the program stepduration 546, however, adjustments can be an increase or a decrease inthe program step duration depending on a desired change in the RWB. Inthe example shown in FIGS. 5A and 5B, the adjustments to the programstep size 554 and the program step duration 556 result in a reduction inthe PET 550; however, embodiments are not so limited.

As described further below, a relationship exists between the adjustmentof a program step size and the adjustment of the program step duration.For instance, the adjustment of the program step size can be in aparticular proportion to the adjustment of the program step durationbased on a relationship between the program step size and the programstep duration. As a result, a RWB can be adjusted by a particular amountby adjusting the program step size and/or duration by particular amountsbased on the determined proportional relationship between step size andstep duration and there respective effects on RWB.

In various embodiments, the RWB can be used as a feedback measure withinthe system, with the adjustment of one or more program stepcharacteristics being used to adjust the RWB toward a target RWBresponsive to a determination that the measured RWB is above or belowthe target RWB. As an example, as a RWB goes above a threshold RWB, aprogram step size and/or a program step duration can be adjusted todecrease the RWB corresponding to a group of cells. Vice versa, as a RWBgoes below a threshold RWB, a program step size and/or a program stepduration can be adjusted to increase the RWB. Dynamically adjusting orcalibrating the programming step size 548 and/or duration 546 to affectthe RWB is described further in association with FIGS. 6-8 below.

FIG. 6 is a graph 600 illustrating how adjusting one or more programstep characteristics affects the read window budget in accordance withsome embodiments of the present disclosure. The graph 600 illustrates alinear relationship between read windows 666-1 to 666-7 and program stepsize corresponding a group of cells each programmed to one of eight Vtdistributions (e.g., respective read windows 336 shown in FIG. 3). Thex-axis of graph 660 represents a program step size offset. As anexample, an offset of “0” can correspond to a default program step size,with each increment or decrement to the offset representing a respectiveincrease or decrease to the program step size (e.g., 10 mV, 100 mV, 1V,etc.). As shown in graph 660, the read windows 666-2 to 666-7 generallydecrease linearly with increased program step size. Accordingly, the RWBcan be adjusted by a known amount by adjusting(incrementing/decrementing) the program step size by a particular offsetamount, which can allow the RWB to be used as a feedback metric in orderto maintain a target RWB, for example.

FIG. 7 is a diagram 769 illustrating how adjusting one or more programstep characteristics affects the read window budget in accordance withsome embodiments of the present disclosure. Curve 774 shown in graph 779illustrates the changes to a RWB 772 (in mV) corresponding to a group ofcells responsive to respective program step size adjustments 770 (e.g.,program step size updates 0 through 20). As an example, the RWB cancorrespond to a summation of respective read windows such as thosedescribed above in FIG. 3 and FIG. 6.

In operation, the program step size adjustments can be made responsiveto determining that a measured RWB is different than a target RWB. Forinstance, in the example shown in FIG. 7, the RWB is between about 2,300mV and 2,500 mV prior to any program step size update. Subsequentprogram step size updates can be made to move the RWB toward the targetRWB, which may be about 2,050 mV, in this example. If the measured RWBis determined to be below the target RWB, then the next subsequentupdate can involve adjusting the step size (e.g., decreasing the stepsize) in order to increase the measured RWB. Conversely, if the measuredRWB is determined to be below the target RWB, then the next subsequentupdate can involve adjusting the step size (e.g., increasing the stepsize) in order to decrease the measured RWB toward the target RWB. Theamount of the step size adjustment associated with the respectiveupdates can be based on a linear relationship such as that described inFIG. 6, for example. Determining an amount of step size adjustment toachieve a particular RWB adjustment is described further below.

FIG. 8 is a diagram 876 illustrating how adjusting one or more programstep characteristics affects the read window budget in accordance withsome embodiments of the present disclosure. Curve 882 shown in graph 876illustrates the changes to a RWB 878 (in mV) corresponding to a group ofcells responsive to respective combined program step size and programstep duration adjustments 879 (e.g., program step size and durationupdates 0 through 20). As an example, the RWB can correspond to asummation of respective read windows such as those described above inFIG. 3 and FIG. 6.

In operation, the program step size and/or program step durationadjustments can be made responsive to determining that a measured RWB isdifferent than a target RWB. For instance, in the example shown in FIG.8, the RWB is greater than 2,200 mV prior to any program step sizeupdate. Subsequent program step size and/or step duration updates can bemade to move the RWB toward the target RWB, which may be about 1,925 mV,in this example. If the measured RWB is determined to be below thetarget RWB, then the next subsequent update can involve adjusting thestep size, the step duration, or both in order to increase the measuredRWB. Conversely, if the measured RWB is determined to be below thetarget RWB, then the next subsequent update can involve adjusting thestep size, the step duration, or both in order to decrease the measuredRWB toward the target RWB. The amount of the step size and step durationadjustments associated with the respective updates can be based on adetermined change needed to null the difference between the measured RWBand the target RWB. Determining an amount of step size and step durationadjustment to achieve a particular RWB adjustment is described furtherbelow. Adjusting both the step time and step duration can providebenefits such as an ability to provide finer RWB adjustments as comparedto methods in which only one or the other of program step size andprogram step duration are adjusted in order to adjust the RWB.

FIGS. 9 and 10 are flow diagrams of example methods corresponding toadjusting a read window budget in accordance with some embodiments ofthe present disclosure. The methods 983 and 1092 can be performed byprocessing logic that can include hardware (e.g., processing device,circuitry, dedicated logic, programmable logic, microcode, hardware of adevice, integrated circuit, etc.), software (e.g., instructions run orexecuted on a processing device), or a combination thereof. In someembodiments, the methods 983 and 1092 are performed by the RWBadjustment component 113 of FIG. 1. Although shown in a particularsequence or order, unless otherwise specified, the order of theprocesses can be modified. Thus, the illustrated embodiments should beunderstood only as examples, and the illustrated processes can beperformed in a different order, and some processes can be performed inparallel. Additionally, one or more processes can be omitted in variousembodiments. Thus, not all processes are required in every embodiment.Other process flows are possible.

At block 986, the processing device (e.g., processing device 112)determines a read window budget (RWB) based on one or more program stepcharacteristics. In some embodiments, program step characteristics caninclude at least one of a program step size or a program step duration,as described herein.

In some embodiments, determining the RWB as illustrated at block 986 canbe performed on a periodic basis, in response to a number of drivefills, a number of program/erase counts, a number of input/output (I/O)operations, input/output workload, and/or a temperature change exceedinga threshold value.

At block 988, the processing device compares the determined RWB to atarget RWB. The target RWB can be provided by an input to the memorysystem. The target RWB can be provided based on an error thresholdand/or other parameters or thresholds that can limit a RWB value. Atblock 990, the processing device, in response to the determined RWBbeing different than the target RWB, adjusts the one or more programstep characteristics that, for example, include at least one of aprogram step size or a program step duration. For example, the memorysystem can increase or decrease the program step size and/or programstep duration, which will correspondingly increase or decrease the RWBby a particular amount based on determined relationships. Either ofthese parameters can be adjusted, or both can be adjusted, to achieve aparticular RWB aligned with the target RWB.

A relationship exists between a program step size and a RWB. Arelationship also exists between a program step duration and the RWB.These relationships can be combined and used to correspond (e.g., in alinear or nonlinear relationship) to the change in RWB with a particularresolution (e.g., a higher resolution). In this example, the change inthe RWB (“DeltaRWB”) can be equal to a change in program step size(“DeltaProgramStep”) plus a change in program step duration(“DeltaProgramTime”), as demonstrated by the formula:

DeltaRWB=DeltaProgramStep+DeltaProgramTime

where a known delta of a program step duration can be equivalent to oneincrement of a program step size. As an example, if one increment of aprogram step size results in a 5% change in RWB and “n” number ofincrements of delta program step duration also results in a 5% change inRWB, then changing the RWB time by 5% can be accomplished by eitherchanging the program step size by one increment or changing the programstep duration by n number of increments. To change the effective programby only 2%, the program step size can remain the same and the programstep duration delta could be adjusted by (2%/5%)*n. To change the RWB by13%, the program step size delta could be 2, resulting in 2*5%=10% plusa change in the program step duration of (3%/5%)*n.

In one example, the two relationships can be treated as linearrelationships. In one example, the two relationships that affect RWBcanbe represented by a formula which can include dependencies andnon-linear effects. In another example, the relationships can berepresented as tables which are indexed in a linear fashion but outputdiffering amounts based on their index. In this example where the deltaprogram step size and the delta program step duration are used as afunction, the combination of the two parameters can be computed for agiven change in RWB. As an example:

[Program Step, ProgramTime]=funcProgramStep_ProgramTime(RWBdelta)

In the example where the delta program step size and the delta programstep duration is used as a table lookup, the combination of the twoparameters can be pre-computed for a given change in RWB, such as inTable 1 below:

TABLE 1 TableIndex ProgramStep ProgramTime RWBdelta 0 −2 0 −2.00 2 −2 7−1.50 3 −1 0 −1.00 5 −1 10 −0.50 6 0 0 0.00 8 0 10 0.50 9 1 0 1.00 11 110 1.50 12 2 0 2.00 14 2 12 2.50Note that the program step duration for the table index of 2 is 7 andthe program step duration for the table index of 14 is 12, illustratinga non-linear relationship.

FIG. 10 is a flow diagram of an example method 1092 for adjusting a readwindow budget (RWB) in accordance with some embodiments of the presentdisclosure. At block 1093, the processing device (e.g., processingdevice 112) determines a read window budget (RWB) based on one or moreprogram step characteristics. In some embodiments, program stepcharacteristics can include at least one of a program step size or aprogram step duration, as described herein.

At block 1094, the processing device compares the determined RWB to aspecific RWB. The specific RWB can be provided by an input to the memorysystem. The specific RWB can be provided based on an error thresholdand/or other parameters or thresholds that can limit a RWB value. Atblock 1095, the processing device, in response to the determined RWBbeing different than the target RWB, adjusts the one or more programstep characteristics that, for example, includes at least one of theprogram step size or the program step duration. Either of theseparameters can be adjusted, or both can be adjusted, to achieve aparticular RWB that can be in line with the specific RWB.

At block 1096, the processing device compares the adjusted RWB to thetarget RWB. At block 1097, the processing device, in response to theadjusted RWB being different than the target RWB, further adjusts theone or more program step characteristics that, for example, includes atleast one of the program step size or the program step duration. As anexample, the initial attempt of adjustment of the RWB from thedetermined RWB to the target RWB can have some errors and this secondcomparison could identify those errors and adjust again. In thealternative, parameters while operating the memory could createanomalies in the memory cells and an adjustment to realign the RWB tothe target RWB can be performed. These anomalies can be created bywearing on the memory cells from many reads and/or writes to and fromthe cells. These anomalies can be created by temperature fluctuationsthat can damage and/or alter the memory cells. Whiles these examples aregiven, examples are not so limited. Any parameters that affect thememory cells and their ability to be programmed could affect the RWB anduse additional adjustment. This repetition of adjustment can beperformed in a dynamic feedback loop where each subsequently adjustedRWB is compared to a previously adjusted RWB in order to fine tune theworking RWB to be the same as the target RWB.

FIG. 11 illustrates an example machine of a computer system 1100 withinwhich a set of instructions, for causing the machine to perform any oneor more of the methodologies discussed herein, can be executed. In someembodiments, the computer system 1100 can correspond to a host system(e.g., the host system 102 of FIG. 1) that includes, is coupled to, orutilizes a memory sub-system (e.g., the memory sub-system 104 of FIG. 1)or can be used to perform the operations of a controller (e.g., toadjust a parameter associated with programming a memory cell, such asprogram step characteristic component 115). In alternative embodiments,the machine can be connected (e.g., networked) to other machines in aLAN, an intranet, an extranet, and/or the Internet. The machine canoperate in the capacity of a server or a client machine in client-servernetwork environment, as a peer machine in a peer-to-peer (ordistributed) network environment, or as a server or a client machine ina cloud computing infrastructure or environment.

The machine can be a personal computer (PC), a tablet PC, a set-top box(STB), a Personal Digital Assistant (PDA), a cellular telephone, a webappliance, a server, a network router, a switch or bridge, or anymachine capable of executing a set of instructions (sequential orotherwise) that specify actions to be taken by that machine. Further,while a single machine is illustrated, the term “machine” shall also betaken to include any collection of machines that individually or jointlyexecute a set (or multiple sets) of instructions to perform any one ormore of the methodologies discussed herein.

The example computer system 1100 includes a processing device 1163, amain memory 1165 (e.g., read-only memory (ROM), flash memory, dynamicrandom access memory (DRAM) such as synchronous DRAM (SDRAM) or RambusDRAM (RDRAM), etc.), a static memory 1167 (e.g., flash memory, staticrandom access memory (SRAM), etc.), and a data storage system 1178,which communicate with each other via a bus 1191.

Processing device 1163 represents one or more general-purpose processingdevices such as a microprocessor, a central processing unit, or thelike. More particularly, the processing device can be a complexinstruction set computing (CISC) microprocessor, reduced instruction setcomputing (RISC) microprocessor, very long instruction word (VLIW)microprocessor, or a processor implementing other instruction sets, orprocessors implementing a combination of instruction sets. Processingdevice 1163 can also be one or more special-purpose processing devicessuch as an application specific integrated circuit (ASIC), a fieldprogrammable gate array (FPGA), a digital signal processor (DSP),network processor, or the like. The processing device 1163 is configuredto execute instructions 1187 for performing the adjustment operationsusing an adjustment component 1173 (including either or both of theprogram step size component and the program step duration componentpreviously described) and steps discussed herein. The computer system1100 can further include a network interface device 1168 to communicateover the network 1180.

The data storage system 1178 can include a machine-readable storagemedium 1184 (also known as a computer-readable medium) on which isstored one or more sets of instructions 1187 or software embodying anyone or more of the methodologies or functions described herein. Theinstructions 1187 can also reside, completely or at least partially,within the main memory 1165 and/or within the processing device 1163during execution thereof by the computer system 1100, the main memory1165 and the processing device 1163 also constituting machine-readablestorage media. The machine-readable storage medium 1184, data storagesystem 1178, and/or main memory 1165 can correspond to the memorysub-system 104 of FIG. 1.

In one embodiment, the instructions 1187 include instructions toimplement functionality corresponding to a program step characteristiccomponent (e.g., program step characteristic component 115 of FIG. 1).While the machine-readable storage medium 1184 is shown in an exampleembodiment to be a single medium, the term “machine-readable storagemedium” should be taken to include a single medium or multiple mediathat store the one or more sets of instructions. The term“machine-readable storage medium” shall also be taken to include anymedium that is capable of storing or encoding a set of instructions forexecution by the machine and that cause the machine to perform any oneor more of the methodologies of the present disclosure. The term“machine-readable storage medium” shall accordingly be taken to include,but not be limited to, solid-state memories, optical media, and magneticmedia.

Some portions of the preceding detailed descriptions have been presentedin terms of algorithms and symbolic representations of operations ondata bits within a computer memory. These algorithmic descriptions andrepresentations are the ways used by those skilled in the dataprocessing arts to most effectively convey the substance of their workto others skilled in the art. An algorithm is here, and generally,conceived to be a self-consistent sequence of operations leading to adesired result. The operations are those requiring physicalmanipulations of physical quantities. Usually, though not necessarily,these quantities take the form of electrical or magnetic signals capableof being stored, combined, compared, and otherwise manipulated. It hasproven convenient at times, principally for reasons of common usage, torefer to these signals as bits, values, elements, symbols, characters,terms, numbers, or the like.

It should be borne in mind, however, that all of these and similar termsare to be associated with the appropriate physical quantities and aremerely convenient labels applied to these quantities. The presentdisclosure can refer to the action and processes of a computer system,or similar electronic computing device, that manipulates and transformsdata represented as physical (electronic) quantities within the computersystem's registers and memories into other data similarly represented asphysical quantities within the computer system memories or registers orother such information storage systems.

The present disclosure also relates to an apparatus for performing theoperations herein. This apparatus can be specially constructed for theintended purposes, or it can include a general purpose computerselectively activated or reconfigured by a computer program stored inthe computer. Such a computer program can be stored in a computerreadable storage medium, such as, but not limited to, any type of diskincluding floppy disks, optical disks, CD-ROMs, and magnetic-opticaldisks, read-only memories (ROMs), random access memories (RAMs), EPROMs,EEPROMs, magnetic or optical cards, or any type of media suitable forstoring electronic instructions, each coupled to a computer system bus.

The algorithms and displays presented herein are not inherently relatedto any particular computer or other apparatus. Various general purposesystems can be used with programs in accordance with the teachingsherein, or it can prove convenient to construct a more specializedapparatus to perform the method. The structure for a variety of thesesystems will appear as set forth in the description below. In addition,the present disclosure is not described with reference to any particularprogramming language. It will be appreciated that a variety ofprogramming languages can be used to implement the teachings of thedisclosure as described herein.

The present disclosure can be provided as a computer program product, orsoftware, that can include a machine-readable medium having storedthereon instructions, which can be used to program a computer system (orother electronic devices) to perform a process according to the presentdisclosure. A machine-readable medium includes any mechanism for storinginformation in a form readable by a machine (e.g., a computer). In someembodiments, a machine-readable (e.g., computer-readable) mediumincludes a machine (e.g., a computer) readable storage medium such as aread only memory (“ROM”), random access memory (“RAM”), magnetic diskstorage media, optical storage media, flash memory components, etc.

In the foregoing specification, embodiments of the disclosure have beendescribed with reference to specific example embodiments thereof. Itwill be evident that various modifications can be made thereto withoutdeparting from the broader spirit and scope of embodiments of thedisclosure as set forth in the following claims. The specification anddrawings are, accordingly, to be regarded in an illustrative senserather than a restrictive sense.

1. A system, comprising: a memory component including a group of memorycells; and a processing device coupled to the memory component andconfigured to: determine a read window budget (RWB) corresponding to thegroup of memory cells, wherein the RWB is a cumulative value of a numberof distances between adjacent threshold voltage distributions associatedwith the group of memory cells at a particular BER; compare thedetermined RWB to a target RWB; and in response to the determined RWBbeing different than the target RWB, adjust one or more program stepcharacteristic to adjust the determined RWB toward the target RWB,wherein the one or more program step characteristics comprises a stepsize that corresponds to a voltage difference between consecutiveprogramming signals of a series of programming signals applied to thegroup of memory cells to program the group of memory cells to aparticular data state.
 2. The system of claim 1, wherein the one or moreprogram step characteristics further comprises a step duration of atleast one of the series of programming signals applied to the group ofmemory cells.
 3. The system of claim 2, wherein the processing device isfurther configured to adjust the step size without adjusting the stepduration of the programming signal to adjust the determined RWB to thetarget RWB.
 4. The system of claim 2, wherein the processing device isfurther configured to adjust the step duration without adjusting thestep size of the programming signal to adjust the determined RWB to thetarget RWB.
 5. The system of claim 1, wherein the memory componentcomprises a plurality of pages and the group of memory cells correspondsto more than one of the plurality of pages.
 6. The system of claim 1,wherein the memory component comprises a plurality of pages and thegroup of memory cells corresponds to a particular page of the pluralityof pages.
 7. The system of claim 6, wherein the particular page israndomly selected from among the plurality of pages.
 8. A method,comprising: determining a read window budget (RWB) corresponding to agroup of memory cells programmed to a particular data state via aprogramming signal having one or more program step characteristics,wherein: an RWB is a cumulative value of a number of distances betweenadjacent threshold voltage distributions associated with the group ofmemory cells at a particular BER; and the one or more programmingcharacteristics comprises a program step duration corresponding to aduration for which the programming signal is applied; comparing thedetermined RWB to a target RWB; in response to the determined RWB beingdifferent than the target RWB, adjusting the one or more program stepcharacteristics to adjust the determined RWB to an adjusted RWB;comparing the adjusted RWB to the target RWB; and in response to theadjusted RWB being different than the target RWB, further adjusting theone or more program step characteristics to adjust the adjusted RWBtoward the target RWB.
 9. The method of claim 8, wherein: the one ormore program step characteristics further comprises a program step size;and the method further comprises decreasing the program step size andthe program step duration each by a respective particular amount inresponse to determining that the determined RWB is less than the targetRWB.
 10. The method of claim 8, wherein: the one or more program stepcharacteristics further comprises a program step size; and the methodfurther comprises increasing the program step size and the program stepduration each by a respective particular amount in response todetermining that the determined RWB satisfies a threshold associatedwith the target RWB.
 11. The method of claim 8, further comprisingrepeating a comparison of a previously adjusted RWB to the target RWB.12. The method of claim 11, wherein the method further comprises, inresponse to the previously adjusted RWB being different than the targetRWB, adjusting the one or more program step characteristics until thepreviously adjusted RWB is the target RWB.
 13. A system, comprising: amemory component including a group of memory cells; and a processingdevice coupled to the memory component and configured to: determine aread window budget (RWB) corresponding to the group of memory cells,wherein the RWB is determined based on respective read windows between aplurality of threshold voltage distributions corresponding to respectivedata states to which the group of memory cells are programmed; comparethe determined RWB to a target RWB; in response to the determined RWBbeing different than the target RWB, adjust one or more program stepcharacteristics by a respective determined amount to adjust the RWBtoward the target RWB. wherein the processing device is furtherconfigured to: determine, using an interpolation, voltages correspondingto two adjacent edges of respective threshold voltage distributions ofthe plurality of threshold voltage distributions at a particular biterror rate (BER), wherein the interpolation is based on a first readlevel voltage whose corresponding BER is lower than the particular BERand a second read level voltage whose corresponding BER is greater thanthe particular BER; use the determined voltages corresponding to the twoadjacent edges to determine a respective one of the read windows; anddetermine the RWB by a summation of the determined read windows. 14.(canceled)
 15. The system of claim 13, wherein the one or more programsstep characteristics comprises a program step size and a program stepduration, and the respective determined amount is based on a determinedrelationship between the program step size and the program stepduration.
 16. The system of claim 13, wherein the processing device isfurther configured to repeatedly adjust the one or more program stepcharacteristics to maintain a constant RWB at the target RWB.
 17. Thesystem of claim 13, wherein the processing device is further configuredto determine the RWB at periodic intervals.
 18. The system of claim 13,wherein the processing device is further configured to determine the RWBresponsive to a determination that the group of memory cells hasexperienced a threshold level of wear cycling.
 19. The system of claim13, wherein the processing device is further configured to determine theRWB responsive to a determination that a temperature change of thememory component has reached a threshold level.
 20. The system of claim13, wherein the processing device is further configured to determine theRWB based on an input/output workload corresponding to the memorycomponent.